1. Field of Invention
The present invention relates to a rod integrator, an illuminator, a projector, and an optical device, and particularly, to a rod integrator suitable for a color-recapture system.
2. Description of Related Art
Various types of projectors have been proposed recently. For single-plate projectors, for example, a sequential color-recapture system (hereinafter, referred to as “a color-recapture system”) has been proposed, such as that described in Sequential Color Recapture and Dynamic Filtering: A Method of Scrolling Color, D. Scott Dewald, Steven M. Penn, and Michael Davis, Texas Instruments Incorporated, (SID 00 DIGEST, 40.2/Dewald). A projector of a color-recapture system includes a light source that supplies white illumination light, a rod integrator for uniformizing the white light from the light source, and a color wheel disposed on an emerging end of the rod integrator for color separation. The rod integrator has an opening for letting the light from the light source in and a reflecting film around the opening, at an incident end face on the light source side. The color wheel has a combination of dichroic films in an appropriate form such as a spiral. The dichroic films transmit light in a specific wavelength range and reflect light in other wavelength ranges. For example, when white light is separated into light in three wavelength ranges, an R-light transmitting dichroic film, a G-light transmitting dichroic film, and a B-light transmitting dichroic film for transmitting only red (R) light, green (G) light, and blue (B) light, respectively, are formed. The color wheel rotates around an axis parallel to the optical axis.
Consider light emitted from the emerging end face of the rod integrator and irradiated to the R-light transmitting dichroic film of the color wheel. Among the white light from the light source, the R light passes through the R-light transmitting dichroic film of the color wheel. On the other hand, the G light and the B light are reflected by the R-light transmitting dichroic film of the color wheel to return toward the light source. The reflected G light and B light are incident on the rod integrator again from the emerging end face. The G light and the B light moving in the rod integrator toward the direction of the light source reach the incident end face. As described above, on the incident end face of the rod integrator, the reflecting film is formed around the opening. Therefore, among the G light and the B light that move in the rod integrator toward the direction of the light source, light incident on the reflecting film is reflected by the reflecting film. The G light and the B light reflected by the reflecting film move in the rod integrator toward the direction of the color wheel and exit from the emerging end face of the rod integrator. The G light and the B light emerging from the emerging end face pass through the G-light transmitting dichroic film or the B-light transmitting dichroic film of the rotating color wheel, without any change, when irradiated thereon. For light that can not pass therethrough, but is reflected by the color wheel, the above-described processes are repeated. Since the color wheel rotates continuously, some light component of the reflected light can pass through the color wheel.
The above description takes the light irradiated to the R-light transmitting dichroic film as an example. The above behavior of light applies also to light emerging from the color wheel and incident on the G-light transmitting dichroic film or the B-light transmitting dichroic film. Accordingly, light loss is reduced, so that light from the light source can be used effectively. This provides efficient color separation and bright color display.